The Intrarater and Interrater Reliability of Glenoid Version and Glenohumeral Subluxation Measurements in Neonatal Brachial Plexus Palsy

Background: Progressive and disabling glenohumeral dysplasia commonly occurs as a secondary deformity in children with neonatal brachial plexus palsy (NBPP). A number of methods for quantifying glenohumeral dysplasia are currently in use; however, the most commonly reported quantitative measures have yet to be validated. The present study assesses the intrarater and interrater reliability of the glenoid version angle (GVA) and percent of the humeral head anterior to the scapular line (PHHA) measurements on axial magnetic resonance images. Methods: Axial magnetic resonance images of the shoulder girdle of 25 children with NBPP were selected to represent a wide range of glenohumeral dysplasia severity. An axial image was preselected for each measurement. Six examiners (3 orthopaedic surgeons, 2 musculoskeletal radiologists, and an epidemiologist) digitally measured the GVA and PHHA on each image twice, with each measurement separated by 2 to 14 days and the order of image presentation placed in a different arrangement for each measurement set. Intrarater and interrater reliability was assessed with the intraclass correlation coefficient (ICC). Measurement errors for the GVA and PHHA measurements and the variances associated with the scapular and glenoid lines were calculated. Results: Using the Fleiss criteria, intrarater reliability was excellent, with ICCs averaging 0.909 (95% CI: 0.840, 0.940) for GVA and 0.891 (95% CI: 0.815, 0.921) for PHHA. Interrater reliability was excellent, with ICCs of 0.848 (95% CI: 0.788, 0.909) for GVA and 0.874 (95% CI: 0.815, 0.934) for PHHA. The GVA and PHHA measurement errors were +/- 6.4 degrees and +/- 7.2%, respectively. In a subset of 141 images measured, the between-image variance in the scapular line was greater than the glenoid line by a 1.61:1 ratio. Conclusions: The present study demonstrates excellent intrarater and interrater reliability of standard measurements of glenohumeral dysplasia in NBPP. The measurement errors for both measurements were comparable with other standard measures (eg, Cobb angle). The scapular line exhibited a greater variance than the glenoid line, which identifies an opportunity for improvement in the GVA measurement. Level of Evidence: Diagnostic study; level III.